Long-term data storage has long been accomplished on such media as magnetic tape and rigid magnetic discs, as well as punched paper cards and tape. More recently, the advent of flexible disc recording technologies have shown the advantages of the inexpensive, limp or "floppy" flexible discs, typically made by coating the opposite sides of a thin, highly flexible sheet of polymeric or other plastic film with magnetic oxide. This limply flexible disc is typically permanently enclosed within a close-fitting, sleeve-like protective outer envelope, in which it may be rotated while the envelope is held in position. The envelope has an enlarged, central opening for access to the center of the disc, and also has a radial slot opening, by which a magnetic head may access the face of the disc while the same is rotated.
A recorder/reproducer apparatus for flexible disc recording is shown in commonly assigned copending applications Ser. No. 418,299 filed Nov. 23, 1973 entitled FLEXIBLE DISC RECORDER CONSTRUCTION, now U.S. Pat. No. 3,913,137, and Ser. No. 518,501 filed Oct. 29, 1974 entitled DISC RECEIVER INTERLOCK FOR DISC RECORDERS, now U.S. Pat. No. 3,973,272.
In disc recorders generally, including those which use flexible discs of the type referred to above, a drive system is required for translational movement of the recording heads across the face of the discs while the latter are rotated. The heads must be advanced incrementally across the discs to predetermined positions, each of which represent an individual narrow, closely spaced, circular recording track on the disc. A common form of such a drive system in disc recorders generally as the voicecoil translator, a form of linear motor. Another system, well-suited for use in flexible disc recorders, comprises a stepper motor which drives a lead screw in incremental steps, with a follower threadedly engaged with the lead screw mounting or coupled to, the recording heads to move the same.
As the heads are positioned in alignment with the various recording tracks, it is important that they be accurately held in place, precisely located with respect to the extremely narrow record tracks. Where stepper motor drives have been utilized in such recorders in the past, the motors, which receive step voltage excitation to drive them in incremental steps, remain energized with a steady excitation to hold them in a given rotational position, and thus maintain the corresponding position of the lead screw and the recording heads, while transducing operations occur in the selected record track. The stepper motor is thus constantly energized, both during stepping or turning operation on the lead screw to advance the head, and also between steps, while transducing operations take place, to maintain the predetermined transducing position. Such constant operation of the stepper motor is a primary source of heat build-up within the apparatus, which is detrimental to the stability and longevity of practically all of the electrical and magnetic components and circuits in the recorder, even including the disc recording media and the motor itself. Nonetheless, positional accuracy for the heads is absolutely essential, and the otherwise undesirable heat build-up has thus heretofore been accepted as an unavoidable consequence, there being no accepted alternatives.